A steel produces a stress corrosion cracking in the presence of hydrogen sulfide or carbonic acid gas. It is believed that a part of hydrogen formed from a reaction of hydrogen sulfide with the steel is absorbed and diffused into the steel in the form of the atomic state to result in the hydrogen embrittlement cracking.
In order to prevent the hydrogen embrittlement, a coating or a lining has been used, by which corrosive reagents such as hydrogen sulfide are prevented from contacting the steel. Typical examples are the method of adding a metallic powder (pigment) reactive with hydrogen sulfide to a coating composition and the method of adding an ion-exchange resin to a coating composition. The former prevents contact between hydrogen sulfide and the surface of the steel by the reaction of hydrogen sulfide with the metallic powder. The latter prevents contact between hydrogen sulfide and the surface of the steel by the reaction of hydrogen sulfide with the ion-exchange resin.
The above methods are based on the reaction of hydrogen sulfide with the additive such as the pigment or the ion-exchange resin. The reaction, however, can not continue forever, that is, the technical effect of the additive would reduce rapidly and the corrosion reaction would begin to increase if the reactivity of the additive decreases. According to the above methods, the corrosion reaction generally begins to increase after 30 hours to 100 days from an application of the coating composition. This term falls short of the actual service life of the steel (50-60 years).